Methods for producing images with the aid of spiral CT units are generally known and are described, for, example, in the relevant chapters of the publications “Computertomographie” [“Computed tomography”], Willi A. Kalender, ISBN 3-89578-082-0 and “Bildgebende Systeme für die medizinische Diagnostik” [“Imaging Systems for Medical Diagnostics”], Heinz Morneburg (Editors), ISBN 89578-002-2, the entire content of the disclosure of which is incorporated herein by reference.
A fundamental distinction is made between so-called 2D and 3D reconstruction methods in the case of the known image producing methods. With reference to the 2D reconstruction method, reference is made by way of example to U.S. Pat. No. 5,802,134 and with reference to the 3D reconstruction method reference is made by way of example to the patent application DE 102 48 770.7, which is not a prior publication, the entire contents each of which being incorporated herein by reference. In the case of both methods, it is known to use spatial weighting functions to take account of the data redundancies occurring during scanning with large conical angles of the beam cone in order to improve the reconstruction method. Patent application DE 102 44 181.2, the entire contents of which is incorporated herein by reference, which introduces such a weighting function W(z) or W(q), z corresponding to the z-axis and q to the number of rows of the multirow detector, may be mentioned by way of example with reference to such a spatial weighting.
The proposed weighting functions all exhibit basically the same behavior. They all have the value 1 in the middle of the detector, and fall off to 0 toward the edge of the detector—seen in the z-direction in each case—in order to avoid artifacts that are caused by the sharp detector edges.
A disadvantage of these weightings resides in the fact that they lead to a reduction in the dose usage.